This disclosure relates to vane pumps. Vane pumps include different varieties such as single acting or double acting and can be fixed or variable displacement. This disclosure is applicable to all types of vane pumps.
A typical double-acting vane pump 10 is depicted in FIG. 1. The vane pump includes a plurality of vanes 12 supported in slots in a rotor 14. A shaft 16 supported concentrically within a cam block 18 rotates the rotor in the direction of arrow 20. The vanes 12 have radial portions 15 and tip portions 17, and are driven outward from the rotor into contact or engagement with an inner surface 22 of the cam block 18. During operation, shaft 16 rotates within the cam block 18 to move each of the vanes 12 about the circumference of the inner surface 22 of the cam block 18. The contour of the cam block inner surface 22 creates radial movement of each of the vanes 12, with the vanes 12 moving into and out of the slots in the rotor 14 as they follow the contour of the cam block inner surface 22
As the vanes move through the inlet regions 24, a quantity of fluid is trapped within a fluid flow chamber defined between the vanes 12 in the direction of rotation and between rotor 14 and the cam block inner surface 22 in the direction the radial direction. The volume of this chamber begins at an initial size that is progressively increased as the vane transitions from inlet region 24 to pump arc 26. In the pump arc 26 the vane 12 extends a constant amount from the rotor 14. As the vane 12 transitions from the pump arc 26 to the discharge region 30, the radial distance between the rotor 14 and the cam block inner surface 22 is gradually decreased. The decrease in volume of the fluid flow chamber coincides with removal of fluid from the flow chamber through the pump discharge. The discharge pressure is dependent upon the resistance of the downstream system
The vanes rotate through pump arcs 26 where high pressure is exerted on the leading surface of the vane and low pressure is exerted on the trailing surface, and through seal arcs 28 where low pressure is exerted on the leading surface of the vane and high pressure is exerted on the trailing surface of the vane. In the inlet regions 24, inlet fluid pressure is provided to support the vanes so that the vanes are radially pressure balanced. In the discharge regions 30, discharge fluid pressure is provided to support the vanes so that the vanes are also radially pressure balanced in the discharge regions.
In the pump arc and the seal arc, pressure has often been required under the vanes to maintain a seal between the vane tip and the cam block inner surface. Such under-vane pressure can combine with pressure in the fluid flow chamber to result in excess radial pressure load and outward centrifugal force pushing the vane against the cam inner surface. This can result in high adhesive wear stresses between the vane tips and the inner surface of the cam block resulting in damage to the vane and to the cam block. However, prior attempts to remove or reduce under-vane pressurization have often resulted in inadequate outward radial load during low speed operation such as at startup, when centrifugal forces are insufficient to drive the vanes radially outward into engagement with the cam block surface.
U.S. Pat. No. 7,637,724 discloses a vane pump where a vane tip 31 has a radius centered on a centerline offset relative to a leading surface of the vane. This offset provides an imbalance of the fluid pressure forces acting radially on the vane tip to generate a positive contact force that in the pump arc that can supplement the centrifugal force at low operating speeds to reduce or eliminate the need for under-vane pressurization in the pump arc. This is depicted in FIG. 2A, where low (inlet) pressure acts on vane surfaces 32, 33, and 34, and high (discharge) pressure acts on vane surfaces 36, 38, and 40. An offset 41 between a centerline 42 of the radial tip 17 and a leading vane surface 44 provides a surface area differential between surfaces 36 and 40 subject high pressure, such that fluid pressure acting on the larger surface 40 and the smaller surface 36 results in a net outward radial load urging the vane into engagement with the cam block inner surface 22. In the seal arcs 26, however, as depicted in FIG. 2B, the larger surface area 40 under the vane tip 31 is not subjected to fluid pressure with the vane in the retracted position. Low (inlet) pressure acts on surfaces 46 and 48, high (discharge) pressure acts on surfaces 33, 50, and 52, and a gradient of pressure acts on surface 53. In the seal arcs 26, the offset 41 now provides a surface area differential of the surfaces subjected to high pressure, between the larger area of surface 50 and the smaller area of under-vane surface 33, resulting in a net radial load inward when the surfaces are subjected to fluid pressure. This necessitates the provision of additional pressurization under the vane in the seal arc, which adds complexity, cost, and weight, in addition to subjecting the under-vane cavities to pressure pulsations.